The ultrasonic field radiated by two­dimensional segmented­annular arrays of unitary aspect ratio, whose driving delays are programmed for spherical focusing, is theoretically studied. The analysis is made in the time domain on the basis of the impulse response function. In this sense, the patterns of the array impulse response at selected field zones are described for the cases of normal radiation and steering. A function describing the time distribution of the elements’ impulse response is helpful for the analysis, because it allows a qualitative description of the main beam. Grating lobes are also analyzed, with the aid of the array periodicity degree concept. From the analysis the following conclusion is reached: the main beam generated by a segmented­annular array is similar to the one produced by a two­dimensional array of squared elements of equivalent dimensions (size and aspect ratio), although segmented­annular arrays produce lower grating lobes. The examples show that an annular segmented array with elements whose size is λ*λ radiates an ultrasonic field of characteristics perfectly valid for volumetric imaging applications.